A challenge for search engine providers is to be able to predict the likelihood that a person will interact with a given item of content. Stated in the context of multiple items of a search results page, one question that arises is: with which of all the search results and/or items of content in a search results page will the person select or interact?
In order to generate probabilities/likelihoods regarding user interaction with any given item of content on a search results page, or a specific item of content, search engine providers utilize and combine a wide range of criteria, conditions, and/or factors into a formula (or set of formulae) to generate the various probabilities and likelihoods of user interaction. However, while the results (probabilistic determinations) of the formulas are determined according to query logs and training models, the formulae are human crafted by one or more persons. These “encoders” select from the various signals (i.e., the criteria, conditions, and/or factors that are available to the search engine in regard to receiving a query) and, based on their expertise and intuition, determine how to interpret, condition, combine and weight the selected signals, and then produce the formula (or formulae) that generates a number representing a probability or likelihood of user interaction.
Obviously, when the formulae are generated according to a particular person's (or group of persons') expertise, experience and intuition, expansion and modifications are also the product of intuition and experimentation. Also, if an encoder leaves the group or company, a void is created and institutional knowledge regarding “how” and “why” a formula is crafted in a certain manner is often lost. For example, if a particular signal is no longer available, or if additional signals become available, modifying a given formula requires the expertise, experimentation, and intuition that was needed to generate the formula in the first place, and the person that originally crafted the formula may or may not still be available to assist. In short, these human-crafted formulae are fragile and unmanageable.